Pillar 3a is tied to Swiss taxation
The principle: the 3a tax deduction requires income taxed in Switzerland. For a cross-border worker, it all depends on your tax status — taxation at source, quasi-resident status, or taxation in your country of residence. Depending on the case, opening a 3a and especially deducting it may be possible, limited, or pointless. This must be checked precisely, as it varies between workers.
When 3a is worthwhile for a cross-border worker
The 3a's main benefit — the tax deduction — only exists if your income is taxed in Switzerland and you can claim that deduction (e.g. via quasi-resident status, under conditions). If you're taxed solely in your country of residence, a Swiss 3a loses most of its tax advantage. Before opening one, review your actual taxation.
Precautions to take
Check your exact tax status (source, quasi-resident, double-taxation treaty) before any contribution, since a 3a you can't deduct loses much of its point. Also consider withdrawal rules if you leave Switzerland, and how it fits with your cross-border 2nd pillar. When in doubt, this is exactly where personalized advice avoids a lasting mistake.